Structure and superconducting properties of a new family of thallium cuprates, TlSr_3-xLn_xCu₂O₇

Abstract

Cuprates of the formula TlSr_3-xLn_xCu₂O₇ (Ln=Pr, NdorY) derived from the hypothetical TlSr₃Cu₂O₇ show superconductivity with T_cs up to 95 K when 0.5 ≤ x ≤ 0.75, the x=1.0 compositions being insulators. Rietveld analysis of X-ray diffraction profiles has been carried out for two superconducting members of this family. The unit cell a-parameter, and hence the in-plane Cu-O distance, increases with increase in x. The T_c value decreases with increase in x or the in-plane Cu-O distance in all the series of cuprates. Superconductivity in the Tl_1-yPb_ySr_3-xNd_xCu₂O₇ systems is found with the highest T_c of 95 K when y=0.2 and x=0.5. The in-plane Cu-O distances in all the cuprates studied fall in the range found in the Sr-class of cuprate superconductors.